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QUIC, the successor to TLS over TCP, has become popular in recent years. Despite its increase in popularity, QUIC has remained largely uncensored: Only Russian TSPU devices analyzed QUIC connections and could extract the server’s hostname from the SNI extension. Other censors—such as China’s GFW—have not been found capable of sophisticated QUIC analysis; in January 2025, we noticed sophisticated QUIC censorship in China.
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Censors worldwide have long censored unencrypted HTTP traffic. In this blog post, we show that a specific HTTP version—unencrypted HTTP/2—is unaffected by censorship in China and Iran. We access otherwise censored websites in both countries over unencrypted HTTP/2. Despite no web browser implementing unencrypted HTTP/2, we detect that up to 6.28% of websites support unencrypted HTTP/2 traffic. To aid the community and ease future research, we provide a tool that evaluates the unencrypted HTTP support of a website. Finally, we discuss the limitations and potential of unencrypted HTTP/2 for censorship circumvention. We consider our finding an interesting addition to current censorship circumvention techniques.
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Last week, Russia started blocking the Encrypted Client Hello (ECH). This prevents Russian internet users from utilizing ECH for censorship circumvention. It also blocks otherwise uncensored websites such as SteamDB. Below, I summarize ECH, detail Russia’s ECH censorship, and discuss possible remedies for affected users and ECH in general.
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TCP fragmentation has long been known as a viable deep packet inspection (DPI) circumvention technique. However, censors are increasingly aware of this technique. We propose TLS record fragmentation as a new censorship circumvention technique on the TLS layer that functions analogously to TCP fragmentation. Using TLS record fragmentation, we successfully circumvented the DPI of the Great Firewall of China (GFW). We also found that over 90% of TLS servers support this new circumvention technique. To contextualize TLS record fragmentation for future work, we discuss its possibilities and limitations.